planck-js/example/Breakable.js

2D JavaScript physics engine for cross-platform HTML5 game development

/*
 * MIT License
 * Copyright (c) 2019 Erin Catto
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

// This is used to test sensor shapes.
planck.testbed('Breakable', function(testbed) {
  var pl = planck, Vec2 = pl.Vec2;
  var world = new pl.World(Vec2(0, -10));

  var breakVelocity;
  var breakAngularVelocity;

  var broke = false;

  // Ground body
  var ground = world.createBody();
  ground.createFixture(pl.Edge(Vec2(-40.0, 0.0), Vec2(40.0, 0.0)), 0.0);

  // Breakable dynamic body
  var body1 = world.createDynamicBody(Vec2(0.0, 40.0), 0.25 * Math.PI);

  var shape1 = pl.Box(0.5, 0.5, Vec2(-0.5, 0.0), 0.0);
  var piece1 = body1.createFixture(shape1, 1.0);

  var shape2 = pl.Box(0.5, 0.5, Vec2(0.5, 0.0), 0.0);
  var piece2 = body1.createFixture(shape2, 1.0);

  world.on('post-solve', function (contact, impulse) {
    if (broke) {
      // The body already broke.
      return;
    }

    // Should the body break?
    var count = contact.getManifold().pointCount;

    var maxImpulse = 0.0;
    for (var i = 0; i < count; ++i) {
      maxImpulse = Math.max(maxImpulse, impulse.normalImpulses[i]);
    }

    if (maxImpulse > 40.0) {
      setTimeout(function() {
        Break();
        broke = true;
      });
    }
  });

  function Break() {
    // Create two bodies from one.
    var center = body1.getWorldCenter();

    body1.destroyFixture(piece2);

    var body2 = world.createDynamicBody(body1.getPosition(), body1.getAngle());

    piece2 = body2.createFixture(shape2, 1.0);

    // Compute consistent velocities for new bodies based on
    // cached velocity.
    var center1 = body1.getWorldCenter();
    var center2 = body2.getWorldCenter();

    var velocity1 = Vec2.add(breakVelocity, Vec2.cross(breakAngularVelocity, Vec2.sub(center1, center)));
    var velocity2 = Vec2.add(breakVelocity, Vec2.cross(breakAngularVelocity, Vec2.sub(center2, center)));

    console.log(velocity1, velocity2);

    body1.setAngularVelocity(breakAngularVelocity);
    body1.setLinearVelocity(velocity1);

    body2.setAngularVelocity(-breakAngularVelocity);
    body2.setLinearVelocity(velocity2);
  }

  testbed.step = function() {
    // Cache velocities to improve movement on breakage.
    if (!broke) {
      breakVelocity = body1.getLinearVelocity();
      breakAngularVelocity = body1.getAngularVelocity();
    }
  };

  return world;
});